“Love is dangerous,” according to Mathieu Amalric. Humorous in fluent English, lithe and demonstrative at the New York Film Festival press Q&A, the “one of our favorites” director, star and cowriter (with costar and life partner of ten years Stéphanie Cléau) was discussing The Blue Room/La chambre bleue.

Adapted from a two-hundred-sixteen-page Georges Simenon novel also done in a Mexican La habitación azul in 2002, the crisp subtitled seventy-six minutes avoids excess, even with a hint of a parallel affaire between a shirtless investigator and stenographer Christelle. Digging into the past to analyze the second, and consequently the first, of two present deaths and concluding with a trial, it wastes no time. In fact, as the filmmaker pointed out, the very first line, “Did I hurt you?” explains in the dark a drop of blood from an act of passion -- another Simenon title -- before the actual visual opening.

Not everything is clarified, he noted, as for instance, the silence of his character Julien’s wife Delphine (Léa Drucker), and -- a nod to Hitchcock -- in the ladder scene there is at least one tease-to-titillate-the-viewer.

The story of entrapment leaves a second murder deliciously ambiguous as to its perpetrator. This Cannes Un Certain Regard is certain to be overshadowed by NYFF companion Opening Night Gone Girl, with which it also shares more than a related idea or two, but the French entry is by much the superior film. Labeled “erotic noir” with its title from the Hôtel de Gare trysting room, it is suggestive even while relatively open in its sex, and Amalric joked about the jokes they used to relax the uneasy undressed Cléau.

In high school, her tall attractive much sought-after Esther had seemed beyond the wildest dreams of his Julien Gahyde, who had moved away from St. Justin for fifteen years and returned just four years ago with a wife and their “fragile” daughter Suzanne (Mona Jaffart). Esther, it turns out, had secretly pined for him way back then, and during his absence married mama’s (Véronique Alain) boy Nicolas Despierre (Olivier Mauvezin) only because he owned a successful pharmacy and was sickly and not liable to live too long.

Returnee Julien runs a John Deere farm vehicle company, has had built a secluded cold modernist home and does his best to avoid Esther. After she gets him into the woods and horizontal without much resistance, they fall into regular sex sessions which begin to scare him while in contrast strengthening her possessive attachment.

SPOILER ALERT

He loosely thinks to break off their liaison, by selling the business and relocating if need be. Whether the mistress realizes his vague intentions or not, she turns deadly, but smilingly and coolly unlike Glenn Close’s fury of a Fatal Attraction woman scorned. One murder leads to another murder, although, whatever a judge may pronounce, we are left to wonder which of three people engineered the second poisoning and why.

Obsessed Esther never gives up, and circumstances, her letters and his bumbling lead to her repentant lover’s being taken into custody, where his interrogation questions are answered with brief flashbacks that may be innocent or deceptive, depending on the read of him. Does he understand, is he a dupe, a villain or only a cowardly would-be ex-adulterer reaping his just, ironic desserts?

(Released by Sundance Selects; not rated by MPAA.)